A rotary offset printing press includes a folding machine which cuts a web into pieces of a predetermined length and folds the web in a width direction and in a length direction, after the web is printed by a print unit and dried and cooled by a drying and cooling unit (see, for example, Patent Literature 1).
Folding methods implemented by the folding machine include: former folding for folding a web before being cut in two in a width direction by a former; single-parallel folding for folding a signature cut from the web in two in a length direction between a folding cylinder and a first jaw cylinder; double-parallel folding (folding in four) for further folding the single-parallel folded signature in two in the length direction between the first jaw cylinder and a second jaw cylinder; delta-folding (rolling folding) for firstly folding a signature, at a one-third position in a width direction, in two in the length direction between the folding cylinder and the first jaw cylinder and then further folding the signature in two in the length direction between the first and second jaw cylinders; and chopper folding for folding the single-parallel folded, double-parallel folded or delta-folded signature in two in a direction parallel to a conveying direction of the signature by use of a chopper. These folding methods are selected to be used independently or in combination according to the specification of the signature.
Here, particularly consider the signature parallel-folded between the folding cylinder and the first jaw cylinder in the folding machine described above. The signature is cut off from a web between a cut-off cylinder and the folding cylinder while a sheet conveying direction end of the signature is being held by needles of the folding cylinder, and then is folded at a center portion by a sucker blade of the folding cylinder and a gripper board of the first jaw cylinder. Thus, even after passing through a contact point (folding position) between the folding cylinder and the first jaw cylinder, the end held by the needles of the folding cylinder is conveyed along a circumferential surface of the folding cylinder to the folding cylinder side. Thereafter, the end is released from the needles of the folding cylinder, and the signature is held at the center portion by the gripper board of the first jaw cylinder and is conveyed toward the first jaw cylinder.
In this way, the end of the signature is conveyed once along the circumferential surface of the folding cylinder to the folding cylinder side, and then is pulled back to and conveyed toward the first jaw cylinder. Thus, the end of the signature (in other words, a trailing edge of a sheet) is conveyed so unstably that the end of the signature may be caught and torn by the following needles of the folding cylinder or may be folded at a corner. The end of the signature similarly is conveyed unstably in a range where the signature is parallel-folded between the first and second jaw cylinders and where the conveying direction end of the signature is similarly pulled back.